1. Field of the Invention
The present invention generally relates to a container holding a liquid and, more particularly, to a mixing container holding at least two liquid constituents in intended proportions. In a preferred form of the present invention, the liquid held in the mixing container is a breathable, cryogenic liquid.
To provide the breathable, cryogenic liquid, a first liquid constituent, predominantly comprising either oxygen or nitrogen, is loaded into the mixing container until it occupies that percentage of the total interior volume intended to hold liquid corresponding approximately to the first liquid constituents known percentage of air. Then, a second, cryogenic liquid constituent, predominantly comprising the other of oxygen or nitrogen, is loaded into the mixing container to completely fill the interior container volume intended to hold liquid. The percentage of the interior volume occupied by the second liquid constituent corresponds approximately to the known percentage of air of the second liquid constituent. The percentages can be adjusted to make the mixture richer in oxygen to insure that the mixture is at least twenty-one percent oxygen and to account for variations in the concentration of the oxygen related to time and other factors.
2. Prior Art
It is known that space requirements and container weight can be substantially reduced for gas storage and delivery systems involving relatively large volumes by maintaining the gas in the more dense liquid phase rather than as a gas or a supercritical fluid. When the liquefied gas is intended to be a breathable gas or in any system intended to contain multi-constituent gases of different boiling points, the conventional practice is to mix the various liquid constituents and store the mixture in a main storage tank. However, when multi-constituent liquefied gases are stored in insulated containers over relatively extended time periods, inevitable heat input to the stored liquid tends to cause evaporation. With multi-constituent liquefied gases of different boiling temperatures, this evaporation will change the relative composition of the stored liquid. Specifically, liquid constituents having lower boiling points will tend to evaporate preferentially resulting in vapor in the container being relatively richer in those constituents with the remaining liquid being leaner in constituents having lower boiling points.
The mixing container of the present invention is an improvement in filling and storing a multi-constituent liquid in that it enables the liquid, for example, a liquefied breathable gas mixture such as liquid air predominantly comprising oxygen and nitrogen to be mixed only at such time as it is anticipated that the breathable gas will be used in the near future. During periods of extended storage, the oxygen and nitrogen liquid constituents can be separately held in dedicated bulk storage containers. That way, the inevitable heat transfer to each of the stored liquid constituents will not result in any change in the composition of the liquid or its gaseous head. Then, at such time as it is anticipated that a liquefied, breathable gas mixture will be needed, the oxygen and nitrogen liquid constituents are filled into the mixing container of the present invention.
The thusly prepared liquid mixture can then be dispensed from the mixing container and gasified for use or, the mixing container can be used to fill the liquid mixture or its gaseous state into other cylinders such as the kind typically used in self-contained breathing apparatus (SCBA) and the like. If the interim period between filling and use is not too prolonged, the liquid and/or gaseous mixture will comprise its constituents within acceptable intended percentages. Also, the present mixing container is constructed such that filling the liquid constituents therein automatically results in a liquid mixture comprising each of the constituents in their intended respective percentages.